The problem isn't really the crackdown as it is that a hero killing a villain is viewed by everyone as jumping off the slippery slope. Which I find kinda hypocritical since heroes are so willing to let villains live and commit more crimes killing more people as long as they have the "moral high-ground". Although to be perfectly fair the civilians of the DC universe do share some of the blame since after all the times the Joker has been brought in and they have not given him the death penalty why, I mean after a certain point you stop being an evil human and are just a monster that needs to be put down.